How a differential gear works (1937) [video] | Hacker News Reader

How a differential gear works (1937) [video]

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391 pointsedferda55 comments

Wow, that was a fantastic video. I could understand it easily only because they iteratively added complexity to the models. It's amazing how well they have made the tutorial for the layman.

Thanks a lot for sharing.

If you liked that, you might like this similar video about how a mechanical watch works:

http://www.youtube.com/watch?feature=player_detailpage&v=508...

Enjoyed watching it. Thanks. :-)

Nice to follow that with this short video illustrating how one type of locking differential works to eliminate some of the disadvantages of an open differential.

https://www.youtube.com/watch?v=MCxqUJCZGNU

So, one wheel starts spinning, and then, at a certain speed, it gets immediately locked into the other wheel which isn't moving at all? How does that not blow up the entire differential?

For manually operated lockers the axle shafts have to be moving at the same speed or with very little difference in speed to be engaged.

>Only engage the Eaton ELocker™ differential while the vehicle is stationary or operating at speeds of 3 mph or less with minimal wheel slippage.

This specific locker (Eaton G80) is self-engaging up to a set speed which is intended to prevent this from happening, though it has been known to occur.

>The G80 can be very effective when used within its limitations. However its very design can lead it to failure. It requires a certain amount of speed difference between both rear wheels to operate. Basically more slip than you would ever encounter going around a turn, but it will not lock at speeds above roughly 20-30mph. This it where it earned the name "gov-lock". It has a speed governor that operates off centrifugal force inside to govern locking.

When it locks, it locks hard. Imagine one tire sitting still, and suddenly being launched to a speed of 20-25mph. That takes a great deal of force and puts a lot of strain on internals. They have a tendency to break with no warning.

Page also has photos of one that has failed.

http://www.ar15.com/forums/t_1_134/1250761_g80_differential_...

With a hard-locking differential ("lockers", generally used off-road), engagement while one wheel is spinning is ill-advised. They're generally toggled on at low/zero speed by the operator in anticipation of a traction-loss situation.

The variety of differential which does not immediately lock one wheel into another is http://en.wikipedia.org/wiki/Limited-slip_differential .

Yup. And they typically have to be unlocked when not needed as it is almost impossible to turn with the rears locked. However, with pneumatic or electrical operation from the driver's seat this is pretty convenient.

The type of locker I'm more familiar with takes a different approach: the rear end is locked by default but unlocks when it needs to. e.g., going around a turn causes the outside tire to turn faster than the inside one, and the teeth in the locker are angled so the speed difference causes them to cam out and decouples one axle shaft from the diff, letting it spin independently while the inner axle shaft is under power.

I had that system in my Toyota pickup and even in 2WD, it was absolutely unstoppable offroad.

I use this video quite often to show an example of one of the best educational videos I have ever seen. The language, presentation, use of graphics (impressive for the time) and demonstrations is just superb.

I like how they start ghost riding the whip at 8:45 https://www.youtube.com/watch?v=K4JhruinbWc#t=519

Around the Corner (1937)

Producer: Handy (Jam) Organization ☞

Sponsor: Chevrolet Division, General Motors Corporation

Probably the source of this re-encode, with significantly less artifacts, on archive.org: https://archive.org/details/Aroundth1937

☞ Named after Jam Handy: https://en.wikipedia.org/wiki/Jam_Handy

If you like videos like this, check out Retrotechtacular on Hackaday. They have a series on mechanical firing computers on navy ship that is nothing short of mech-eng porn, and I mean the classy kind.

That was amazing, thanks. I found the integrator and multiplier especially simple and clever.

Here is a link to a youtube playlist: https://www.youtube.com/user/navyreviewer/videos?query=mecha...

I watched that whole series a year ago and was fascinated. I believe it has been posted here before but it's worth repeating.

My favorite: Wave Behavior from Bell Labs: https://www.youtube.com/watch?v=DovunOxlY1k

Excellent use of graphics, created in the age before computer graphics.

A World War 2 training video for evading flak cannon fire is one of the best examples of graphical information presentation that I've seen. https://www.youtube.com/watch?v=qP_-WUMi-nw

It features smoothly animated and highly functional designs as well as overlaying graphics on real footage to achieve a fashion of "augmented reality". The production quality is astounding and it is amazing to think that it was produced in the 40s. The entire video is an inspiring example of conveying information.

That was really interesting. I never knew there was this kind of strategy behind flak evasion. Man, must have taken some stones to do a bomber mission. I knew an old timer that flew bombers in WW2 and he said towards the end of the war the germans were running out of metal and all sorts of things were used as flak. He said nuts and bolts were pretty common. He'd find them embedded inside the cabin after close flak fire. Pretty scary to think that your end might come from a washer.

RAF Bomber Command had appalling rates of attrition through WWII.

http://en.m.wikipedia.org/wiki/RAF_Bomber_Command

The wiki article gives good explanation of how bombing developed during WWII - starting as a weapon to terrible to be used (based on poor quality data); with general agreements not to kill civilians; realising that bombers were hopelessly inaccurate; changing tactics to allow bombing of civillian populations, including the (to my mind) war crimes of fire bombing.

> Bomber Command crews also suffered an extremely high casualty rate: 55,573 killed out of a total of 125,000 aircrew (a 44.4% death rate), a further 8,403 were wounded in action and 9,838 became prisoners of war.

That's pretty much "toss a coin".

Thank you for posting this.

Wow! Amazing.

There's another video from 1949 about 'How a Watch Works' — http://www.youtube.com/watch?v=508-rmdY4jQ

I had not seen this particular video but have seen the "How a manual transmission works" from the same series.

https://www.youtube.com/watch?v=aAWxZRuBXtw

An interesting mechanism using differential gears, doubling the speed while only using gears of the same size:

http://507movements.com/mm_226.html

The way the teaching was sequential really made it an understandable to a layman like myself.

There's a chap who collects tons of videos like this on YouTube. He was mentioned on MetaFilter the other day: http://www.metafilter.com/143903/Do-you-like-vintage-trainin...

Or you can find his channel direct on https://www.youtube.com/user/webdev17/videos

This is the best technical education video I've ever seen. If all information were available in such an easy to understand form, the world would be full of geniuses.

The level of effort is astounding. The "support" part holding the spokes looks cast. They couldn't have possibly cast that part specifically for this video... could they?

casting one-offs with a disposable form (wax, styrofoam) isn't particularly difficult or expensive. They use big basins full of super-fine sand: a great insulator and the grains are too tightly packed for the liquid metal to flow into the tiny spaces between them. We used to do it in high school shop class.

Brilliant video. It's definitely a lot better to see the basic principles and evolution of those principles in action.

I remember reading through David Macaulay's “The Way Things Work” as a kid, soaking up the illustrations until I understood each one. It was life-changing. However, I remember having trouble with one page in particular -- the one describing differential gears. Of course, video would probably have helped a lot :)

I remember seeing this a while back and realizing I learned more from this video than I learned in class during my college course. Amazing production value. We should properly catalog such gems so that students and even professors can use these to teach (instead of attempting to reinvent the wheel)

I'd like to see a Torsen gearcase. Strange little things, they look like pepper grinders.

I remember building lego cars which had a differential: http://groups.csail.mit.edu/drl/courses/cs54-2001s/images/le...

The actual explanation doesn't start until about 2 minutes in: https://www.youtube.com/watch?v=K4JhruinbWc#t=110

I was generally not bad at physics but I remember not getting my head around this one...

What a great lesson for decoupling systems. I wonder what's the software equivalent in design pattern land. The facade maybe ?

Not sure about a corresponding design pattern, but the content neatly maps (no pun intended) to function composition.

I never really got my head around electricity and magnetism. That stuff is very abstract.

some may also enjoy a 3d-printed triple gear

https://www.youtube.com/watch?v=I9IBQVHFeQs

Does this have any possible practical applications? Or is it just cool?

Is it possible to create a "negative differential gear" that puts more torque into the wheel that is stuck? (in the hopes of forcing it unstuck)

Yes. You are referring to a locking differential, of which there are several types. Some use clutch plates, and will work even if one wheel has no traction at all, others use more complex gearing and can transfer torque from one to another at some multiple (called a Torsen Differential) and cannot drive when one wheel is completely unloaded.

Awesome, thank you!

It is just too awkward that I learned how they work with the same video last year, still better than my University's current presentations

Differential -- the most misused word in sports. The video is a great explanation about the automobile version.

I'd have loved it if these guys had made a video on fly wheels. Dying to know more about those.

@edferda: props for posting this; the pedagogy here is just terrific!

Any idea for what purpose was this video originally made?

I guessed some of the next steps, and considering I have the automobilic knowledge of the ancient greeks, that was pretty impressive.

An education in how to present to a lay audience.

love the clarity, simplicity and enunciation

Great Video:)

Best spent 8minutes today, thanks!

Interesting

Amazing!

We know. I put a link to that video (to the Internet Archive, not YouTube) on Wikipedia years ago.

There's a whole series of Chevrolet films from the Jam Handy organization at the Internet Archive. "Take it Easy", "Spring Harmony" and "Shockproof" cover how auto suspensions work. "Facts on Friction", "Hydraulics" and "What stops them" explain brakes. "Head on" and "No Ghosts" - auto frames. "Water Boy" - cooling. "Free Air" - carburetor. There's more.

I had never seen this, so i appreciate the link. Is there any similar video for a limited slip differential?

Here's a good start. Alter search query to taste.

https://archive.org/search.php?query=creator%3A%22Handy%20%2...

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